Single row deep groove radial ball bearing

ABSTRACT

The radius of curvature r 1 , r 2  of the cross-sectional shape of an inner ring raceway  11   d  is made smaller at a central portion  19  and larger at end portions  20 . A contact ellipse at the end portions is made small by increasing the radius of curvature r 2  of the end portions  20  to thereby secure an allowable moment load. In contrast with this, an angular gap is reduced by reducing the radius of curvature r 1  of the central portion  19.

This is a continuation of Application Ser. No. 09/772,957 filed Jan. 31,2001, now U.S. Pat. No. 6,554,480; the disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

A single row deep groove radial ball bearing according to the presentinvention is used to support a rotary member such as a pulley and toremovably support an offset load.

Automotive accessories such an alternator and a compressor are driven torotate by an engine for driving a vehicle. Due to this, an endless beltis extended between follower pulleys fixed to end portions of rotatingshafts of the automotive accessories and a drive pulley fixed to an endportion of a crankshaft of the driving engine, and the rotating shaftsare constructed to be driven to rotate based on the circulation of theendless belt.

FIG. 5 illustrates the construction of a rotational driving portion of arotating shaft 1 of a compressor constituting an automotive airconditioner. The rotating shaft is rotatably supported by rollingbearings, not shown, within a casing 2. A follower pulley 4 is rotatablysupported around the circumference of a supporting tube portion 3provided on an outer circumference of an end portion of the casing 2 bya single row deep groove radial ball bearing 5. The follower pulley 11is formed into an annular configuration, on the whole, which hassubstantially a U-shaped cross section, and a solenoid 6 which is fixedto an end face of the casing 2 is disposed within an internal space ofthe follower pulley 4. On the other hand, a mounting bracket 7 is fixedto a portion protruding from the casing 2 at an end portion of therotating shaft 1, and an annular plate 21 of a magnetic material issupported on the circumference of the mounting bracket 7 via a platespring 8. The annular plate 21 is spaced away from the follower pulley4, as shown in FIG. 5, when the solenoid 6 is not energized, while whenthe solenoid 6 is energized, the annular plate 21 is drawn toward thefollower pulley 4 so as to be secured thereto, so that a rotationalforce is free to be transmitted from the follower pulley 4 to therotating shaft 1.

With the rotational supporting device as described above, there may be acase where a transverse central position (a chain line α in FIG. 5) ofthe endless belt wound around an outer circumference of the followerpulley 4 is not allowed to coincide with a transverse central position(a chain line β in FIG. 5) of the single row deep groove radial ballbearing 5. In such a case, a moment load in proportion to a deviatingamount (offset amount) δ between the transverse central positions of thetwo members is applied to the single row deep groove radial ball bearing5 based on the tension of the endless belt. Then, a central axis of aninner ring 9 and a central axis of an outer ring 10 which constitute thesingle row deep groove radial ball bearing 5 do not coincide with eachother (they are inclined).

With a mechanism like one as described above, when the central axes ofthe inner ring 9 and the outer ring 10 do not coincide with each other,there occurs an unbalanced wear of the endless belt which is woundaround the outer circumference of the follower pulley 4, this making itdifficult to secure the durability of the endless belt. In addition, theinclination of the central axes also makes it impossible to secure acertain gap between the annular plate 21 and the follower pulley 4,resulting in a possibility that these two members 21, 4 come intofriction with each other. In the event that such a friction occurs,abnormal wear and abnormal noise are likely to be generated unfavorably.With a view to preventing the occurrence of these inconveniences, it isconsidered to reduce an angular gap of the single row deep groove radialball bearing 5 in order to make it difficult that the central axes ofthe inner ring 9 and the outer ring 10 discord with each other.

Then, in order to reduce the angular gap for the aforesaid purpose, thefollowing (1) to (4) procedures will be contrived.

(1) Radius of curvatures of cross-sectional shapes of an inner ringraceway 11 formed in an outer circumferential surface of the inner ring9 and an outer ring raceway 12 formed in an inner circumferentialsurface of the outer ring 10 are made small (they are to be reduced soas to approximate 50% of the outside diameter of balls 13 constitutingthe single row deep groove radial ball bearing 5).

(2) As shown in FIG. 6, the raceway surface of one or both of an innerring raceway 11 a in an outer circumferential surface of an inner ring 9a and an outer ring raceway 12 a in an inner circumferential surface ofan outer ring 10 a is formed into a combined surface, and rollingsurfaces of balls 11 are brought into contact with both the racewaysurfaces at three or four points.

(3) As shown in FIG. 7, the heights of shoulder portions 14 a, 14 bexisting on transverse (in left and right directions in FIG. 7) sides ofthe raceway surface of one or both of an inner ring raceway 11 b in anouter circumferential surface of an inner ring 9 b and an outer ringraceway 12 b in an inner circumferential surface of an outer ring 10 bare made higher as indicated by a solid line than a general heightindicated by a chain line in the same figure.

(4) As shown in FIG. 8, a plural row radial ball bearing 15 is used inwhich a plurality of balls 13, 13 are provided between a plurality ofinner ring raceways 11 c, 11 c formed in an outer circumferentialsurface of an inner ring 9 c and between a plurality of outer ringraceways 12 c, 12 c formed in an inner circumferential surface of anouter ring 10 c, respectively.

The conventionally known and contrived constructions for reducing theangular gap as described above have the following problems.

First of all, in the case of the construction described under (1),although the angular gap can be reduced, the contact ellipses existingat abutting portions of the rolling surfaces of the respective balls andthe inner ring raceway 11 and the outer ring raceway 12 become larger.Then, the contact ellipses dislodge from the inner ring raceway 11 andthe outer ring raceway 12 when the central axes of the inner ring 9 andthe outer ring 10 are only inclined slightly by virtue of a moment load.In this state, the rolling fatigue life of the rolling surface becomesextremely short. Thus, the construction described under (1) is notdesirable as the allowable moment load becomes small. Note that whilethe configurations of the contact portions can be ellipse no more(resulting in a configuration in which part of the ellipse becomes lost)when the contact portions between the rolling surfaces and the racewaysurfaces reach the transverse end edges of the raceway surfaces, for thepurpose of description, a state like this will be referred to as “thecontact ellipse dislodges from the raceway surface” in thisspecification.

Next, with the construction described under (2), the rolling surfaces ofthe balls 13 and the inner ring raceway 11 a and the outer ring raceway12 a come to contact with each other at a plurality of contactpositions, and moreover, in a state in which the engine is driven whilethe moment load is applied, since the contact positions becomeasymmetrical relative to the rotating axis of the ball 13, there occurmuch wear and heat based on slippage at the contact points, which is notdesirable.

Next, with the construction described under (3), since the space betweenthe shoulder portions 14 a, 14 a on the outer circumferential surface ofthe inner ring 9 b and the shoulder portions 14 b, 14 b on the innercircumferential surface of the outer ring 10 b becomes narrow, thediametrical thickness of a retainer 16 for holding the balls 13 becomesthin. Thus, as the thickness of the retainer 16 becomes thin, since itis difficult to secure the durability of the retainer 16, inconsideration of the durability of the retainer 16, the effect ofreducing the angular gap using the procedure described under (3) islimited.

Furthermore, with the construction described under (4), although theeffect of reducing the angular gap and securement of the durability ofthe constituent components becomes compatible at a higher order, theincrease in axial dimension cannot be avoided. The rotational supportingportion such as the follower pulley 4 has to be installed within alimited space in many cases, and therefore the increase in axialdimension is not desirable. Moreover, as the axial dimension increases,the production cost of the respective constituent components alsoincreases.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a single row deepgroove radial ball bearing which can solve the inconveniences asdescribed above.

Similarly to single row deep groove radial ball bearings conventionallywidely known, any of single row deep groove radial ball bearingsaccording to the invention comprises an inner ring having a deep grooveinner ring raceway formed in an outer circumferential surface thereof,an outer ring having a deep groove outer ring raceway formed in an innercircumferential surface thereof and a plurality of balls rotatablyprovided between the inner ring and the outer ring.

In particularly, in the single row deep groove radial ball bearingaccording to the present invention, at least one of the inner ringraceway and the outer ring raceway has a cross-sectional shape in whicha transversely central portion thereof is different in a radius ofcurvature from transverse end portions between which the transverselycentral portion is interposed, and also transverse end edges of theportions having different radius of curvatures are made to be smoothlycontinuous with each other.

In the above-mentioned single row deep groove radial ball bearing as setforth in the invention, it is advantageous that the radius of curvatureof the cross-sectional shape of at least one (or preferably, both) ofthe inner ring raceway and the outer ring raceway is made smaller at atransversely central portion and larger at transverse end portions, andtransverse end edges of the portions having different radius ofcurvatures are made to be smoothly continuous with each other.

According to the single row deep groove radial ball bearings constructedas described above in accordance with the invention, the reduction ofthe angular gap and securement of the allowable moment load can beestablished at a higher order.

First of all, with the single row deep groove radial ball bearing as setforth in the invention, since the radius of curvature of thecross-sectional shape of the raceway is made larger at the transverseend portions, in the event that the central axis of the inner ring andthe central axis of the outer ring are inclined toward each other basedon the moment load, and that the contact point between the rollingsurface of the ball and the raceway is displaced to the transverse endportion side of the raceway, the contact ellipse existing at the contactpoint becomes small. Due to this, it is difficult for the contactellipse to dislodge from the raceway, the allowable moment load can besecured. Moreover, since the radius of curvature of the cross-sectionalshape of the transversely central portion of the raceway is madesmaller, when compared with a case where the entirety of the racewayconstitutes a single curved surface having a large radius of curvature,the rolling surface of the ball and the raceway are allowed to getcloser to each other to thereby reduce the angular gap.

Furthermore, in the above-mentioned single row deep groove radial ballbearing as set forth in the invention, it is advantageous that theradius of curvature of the cross-sectional shape of at least one (orpreferably, both) of the inner ring raceway and the outer ring racewayis made larger at a transversely central portion and smaller attransverse end portions, and transverse end edges of the portions havingdifferent radius of curvatures are made to be smoothly continuous witheach other.

According to the single row deep groove radial ball bearings constructedas described above in accordance with the other aspect of the invention,the reduction of the angular gap and securement of the allowable momentload can be established at a higher order.

With the single row deep groove radial ball bearing as set forth in theinvention, since the radius of curvature of the cross-sectional shape ofthe raceway is made smaller at the transverse end portions, whencompared with the single curved surface having a large radius ofcurvature, the rolling surface of the ball and the raceway are allowedto get closer to each other to thereby reduce the angular gap. In thiscase, too, since the radius of curvature of the cross-sectional shape ofthe raceway is made larger at the transversely central portion, even inthe event that the central axis of the inner ring and the central axisof the outer ring are inclined toward each other based on the momentload, and that the contact point between the rolling surface of the balland the raceway is displaced to the transverse end portions of theraceway, it is difficult for the contact ellipse to dislodge from theraceway to thereby secure the allowable moment load.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a partial sectional view illustrating a first embodiment ofthe invention;

FIG. 2 shows an enlarged view illustrating an X portion of FIG. 1;

FIG. 3 shows a similar view to FIG. 2, illustrating a second embodimentof the invention;

FIG. 4 shows a similar view to FIG. 2, illustrating a third embodiment;

FIG. 5 shows a partial sectional view of a rotational supportingportion, illustrating an exemplary state in which a single row deepgroove radial ball bearing;

FIG. 6 shows a partial sectional view illustrating a first example of aconventional single row deep groove radial ball bearing;

FIG. 7 shows a partial sectional view illustrating a second example ofthe same; and

FIG. 8 shows a partial sectional view illustrating a rotationalsupporting portion constituted by a double-row ball bearing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2 illustrate a first embodiment corresponding to theinvention. Similarly to the conventionally well known single row deepgroove radial ball bearings, a single row deep groove radial ballbearing 5 a according to the invention comprises an inner ring 9 d, anouter ring 10 d and a plurality of balls 13. The inner ring 9 d has adeep groove inner ring raceway 11 d formed in an outer circumferentialsurface thereof. The outer ring 10 d has a deep groove outer ringraceway 12 d formed in an inner circumferential surface thereof. Theplurality of balls 13 are rotatably provided between the inner ringraceway 11 d and the outer ring raceway 12 d. In addition, the pluralityof balls 13 are retained by a retainer 16 a so as to roll freely.Openings at ends of an annular space 17 formed between the outercircumferential surface of the inner ring 9 d and the innercircumferential surface of the outer ring 10 d are closed with sealplates 18, 18, respectively.

In particular, in the single row deep groove radial ball bearing 5 aaccording to the invention, the radius of curvatures of thecross-sectional shapes of the inner ring raceway 11 d and the outer ringraceway 12 d are made smaller at the transversely (in left and rightdirections in FIG. 1) central portions and larger at the transverse endportions of the respective raceways, and the transverse end edges of theportions having the different radius of curvatures are made to besmoothly continuous with each other. In other words, as shown in detailby a solid line X in FIG. 2, the cross-sectional shape of the inner ringraceway 11 d is constituted by a central portion 19 having a radius ofcurvature r1 and a pair of end portions 20, 20 each having a radius ofcurvature of r2. In this embodiment, the cross-sectional shapes of theinner ring raceway 11 d and the outer ring raceway 12 d are basicallythe same, and therefore, the cross-sectional shape of the inner ringraceway 11 d shown in FIG. 2 will be described.

With the present embodiment, the radius of curvature r2 of each of theend portions 20, 20 is made larger than the radius of curvature r1 ofthe central portion 19 (r2>r1). The central portion 19 is formed througha central angle of α (for example, in the order of 25 to 35 degrees) oneach side of a center line relative to the transverse direction which isindicated by a chain line y in FIG. 2, and therefore as a whole, thecentral portion 19 is formed over a total central angle of 2α across thecenter line. The radius of curvature r1 of this central portion 19 ismade slightly larger than 50% of the outside diameter of the ball 13(for example, in the order of 50.5 to 52%, preferably 51 to 52%). Incontrast to this, the respective end portions 20, 20 are formed througha central angle of β (for example, in the order of 25 to 35 degrees) oneach side of the central portion 19 (in such a manner as to hold thecentral portion 19 therebetween). The radius of curvature r2 of each ofthe end portions 20, 20 is made a bit larger than 50% of the outsidediameter of the ball (for example, in the order of 53 to 55%, preferably53 to 54%).

Then, the transverse end edges of the central portion 19 and thetransverse inner end edges of the respective end portions 20, 20 aremade to be smoothly continuous with each other, respectively, at aportion indicated by a point A in FIG. 2. Due to this, in thisembodiment, the tangential direction of an arc having the radius ofcurvature r1 and the tangential direction of an arc having the radius ofcurvature r2 are caused to match with each other.

In other words, the central portion 19 and the respective portions 20has a common tangential line at a connecting portion A therebetween.

According to the single row deep groove radial ball bearing of thepresent embodiment which is constructed as described above, thereduction of the angular gap and securement of the allowable moment loadare compatible at a higher order. Namely, with the single row deepgroove radial bearing 5 a according to the present embodiment, theradius of curvatures of the cross-sectional shapes of the inner ringraceway 11 d and the outer ring raceway 12 d are made to be a relativelylarger radius of curvature r2 at the transverse end portions 20, 20.Consequently, even if the center axis of the inner ring 9 d and thecenter axis of the outer ring 10 d are inclined towards each other basedon the moment load and the contact point between the rolling surface ofthe ball 13 and the inner ring raceway 11 d and the outer ring raceway12 d is displaced toward the transverse end portion side, whereby therolling surface of the ball 13 contacts the transverse end portions 20,20, the contact ellipse existing at the contact portion is small. Due tothis, it is difficult for the contact ellipse to dislodge from the innerring raceway lid and the outer ring raceway 12 d, thereby making itpossible to secure the allowable moment load.

In other words, in a case where the cross-sectional shapes of the innerring raceway 11 d and the outer ring raceway 12 d are made to be asingle curved surface having the relatively small radius of curvaturer1, as shown by a broken line Y in FIG. 2, the radius of curvature r1remains as small as it is to a continuous portion with the shoulderportion 14 a (14 b) of the inner ring 9 d and the outer ring 10 d. Then,even in a state in which the rolling surface of the ball 13 is incontact with a portion in the vicinity of the shoulder portion 14 a (14b), the contact ellipse existing at the contact portion remains large,and it becomes easy for the contact ellipse to dislodge from the innerring raceway 11 d and the outer ring raceway 12 d, thereby making itdifficult to secure the allowable moment load. In contrast with this,with the present embodiment, as described above, in the state in whichthe rolling surface of the ball 13 is in contact with the portion in thevicinity of the shoulder portion 14 a (14 b), since the contact ellipseexisting at the contact portion becomes small, it is possible to securethe moment load as described above.

Moreover, since the radius of curvature r1 of the transversely centralportion 19 of the cross-sectional shape of the inner ring raceway 11 dand the outer ring raceway 12 d is small, when compared with a casewhere the entirety of the inner ring raceway 11 d and the outer ringraceway 12 d is made to be a single curved surface having a large radiusof curvature, the rolling surface of the ball 13 can get closer to theinner ring raceway 11 d and the outer ring raceway 12 d to therebyreduce the angular gap.

Namely, in a case where the cross-sectional shapes of the inner ringraceway 11 d and the outer ring raceway 12 d are made to be a singlecurved surface having the relatively large radius of curvature r2, asshown by a chain line Z in FIG. 2, the radius of curvature r2 remains aslarge as it is to the continuous portion with the shoulder portion 14 a(14 b) of the inner ring 9 d and the outer ring 10 d. Due to this, thegap between the rolling surface of the ball 13 and the two raceways 11d, 12 d becomes larger at the transverse end portions of the inner ringraceways 11 d and the outer ring raceway 12 d, and thus, the angular gapcannot be reduced. In contrast with this, with the present embodiment,as described above, since the radius of curvature r1 of the transverselycentral portion 19 of the cross-sectional shape of the inner ringraceway 11 d and the outer ring raceway 12 d is made small, the gapbetween the rolling surface of the ball 13 and the two raceways 11 d, 12d can be reduced at even at the transverse end portions of the innerring raceway 11 d and the outer ring raceway 12 d, thereby making itpossible to reduce the angular gap.

Next, FIG. 3 illustrates a second embodiment corresponding to a secondaspect of the invention. In the present embodiment, the radius ofcurvature of the cross-sectional shape of an inner ring raceway lie (anouter ring raceway) is made lager at a transversely central portion 19 aand smaller at transverse end portions 20 a. Note that in thisembodiment, too, since the cross-sectional shapes of the inner ringraceway lie and the outer ring raceway, not shown, are basicallyidentical, the cross-sectional shape of the inner ring raceway shown inFIG. 3 will only be described below.

In this embodiment, the radius of curvature r1′ of each of the endportions 20 a is made smaller than the radius of curvature r2′ of thecentral portion 19 a (r2′>r1′). The central portion 19 a is formedthrough a central angle of α′ (for example, in the order of 25 to 35degrees) on each side of a center line relative to the transversedirection which is indicated by a chain line y in FIG. 3, and thereforeas a whole, the central portion 19 a is formed over a total centralangle of 2α′ across the center line. The radius of curvature r2′ of thiscentral portion 19 a is made a bit larger than 50% of the outsidediameter (FIG. 1) of the ball 13 (for example, in the order of 53 to55%, preferably 53 to 54%). In contrast with this, the respective endportions 20 a are formed through a central angle of β′ (for example, inthe order of 25 to 35 degrees) on each side of the central portion 19 a(in such a manner as to hold the central portion 19 a therebetween). Theradius of curvature r1′ of each of the end portions 20 a is madeslightly larger than 50% of the outside diameter of the ball 13 (forexample, in the order of 50.5 to 52%, preferably 51 to 52%).

Then, the transverse end edges of the central portion 19 a and thetransverse inner end edges of the respective end portions 20 a are madeto be smoothly continuous with each other, respectively, at a portionindicated by a point A′ in FIG. 3. Due to this, in this embodiment, thetangential direction of an arc having the radius of curvature r2′ andthe tangential direction of an arc having the radius of curvature r1′are caused to match with each other.

In other words, the central portion 19 a and the respective portions 20a has a common tangential line at a connecting portion A′ therebetween.

In the single row deep groove radial ball bearing of the invention whichis constructed as described above, since the radius of curvatures of thecross-sectional shapes of the inner ring raceway 11 e and the outer ringraceway, not shown, are made to be the smaller value r1′ at thetransverse end portions 20 a, when compared with a single curved surfacehaving the larger radius of curvature r2′, the rolling surface of theball and the relevant raceway can get closer to each other to therebyreduce the angular gap.

Namely, in a case where the cross-sectional shapes of the inner ringraceway lie and the outer ring raceway are a single curved surfacehaving the relatively larger radius of curvature r2′, as shown by achain line D in FIG. 3, the radius of curvature r2′ remains as large asit is to the shoulder portion 14 a of the inner ring 9 e and the outerring, not shown. Due to this, the gap between the rolling surface of theball 13 and the two raceways 11 e becomes large at the transverse endportions of the inner ring raceway 11 e and the outer ring raceway, notshown, and therefore, the angular gap cannot be reduced. In contrastwith this, with the present embodiment, as described above, since theradius of curvature r1′ of the transverse end portions 20 a of thecross-sectional shapes of the inner ring raceway 11 e and the outer ringraceway, not shown, is made smaller, the gap between the rolling surfaceof the ball 13 and the two raceways 11 e can be reduced even at thetransverse end portions of the inner ring raceway 11 e and the outerring raceway, thereby making it possible to reduce the angular gap.

Even in this case, since the radius of curvature of the cross-sectionalshapes of the inner ring raceway 11 e and the outer ring raceway, notshown, is made larger at the transverse end portions 19 a, even in theevent that the center axis of the inner ring 9 e and the center axis ofthe outer ring, not shown, are inclined toward each other based on themoment load and that the contact point between the rolling surface ofthe ball 13 and the inner ring raceway 11 e and the outer ring raceway,not shown, is displaced toward the transverse end portion side of theinner ring raceway 11 e and the outer ring raceway, not shown, itbecomes difficult for the contact ellipse to dislodge from the innerring raceway 11 e and the outer ring raceway, not shown, to therebysecure the allowable moment load. In addition, the construction of thepresent embodiment can suppress the generation of heat at normal times(in a state in which the center axes of the inner and outer ringscoincide with each other) when it is applied to an application in whichonly a relatively small moment load is applied such as a case where anintermediate pulley for guiding an endless belt is rotatably supported,and the construction can also be used for an application in which theangular gap is to remain as small as possible.

Next, FIG. 4 illustrates a third embodiment of the invention. In eitherof the aforesaid first and second embodiments, while the two differentradius of curvatures are used for the cross-sectional shapes of theinner ring raceway 11 d, 11 e and the outer ring raceway 12 d, in thisembodiment, there are provided more different radius of curvatures r1,r2, r3. . . rn for use for the cross-sectional shapes of an inner ringraceway 11 f. In a case where the present embodiment is used to carryout an aspect of the invention corresponding to the first aspectthereof, the radius of curvature is made to become larger as itapproaches a shoulder portion 14 a (r1<r2<r3<. . . <rn), while when usedto carry out an aspect of the invention corresponding to the secondaspect thereof, the radius of curvature is made to become smaller as itapproaches the shoulder portion 14 a (r1>r2>r3>. . . >rn).

While there has been described in connection with the preferredembodiment of the invention, it will be obvious to those skilled in theart that various changes and modifications may be made therein withoutdeparting from the invention, and it is aimed, therefore, to cover inthe appended claim all such changes and modifications as fall within thetrue spirit and scope of the invention.

Since the single row deep groove radial ball bearing according to theinvention is constructed and operates as has been described heretofore,there is no need to increase the axial dimension, and moreover, thegeneration of heat and wear can be suppressed which would otherwise begenerated when the engine is running. Due to this, with the invention,it is possible to suppress the inclination of a member that is to besupported by the single row deep groove balling such as a pulley tothereby extend the life of a belt. Thus, the invention can contribute tominiaturizing various types of mechanical devices having a rotationalsupporting portion and increasing performances thereof. In addition, theinvention can prevent the friction contact of constituent components ofan electromagnetic clutch when it is switched off to thereby prevent thegeneration of abnormal wear and noise.

What is claimed is:
 1. A single row deep groove radial ball bearingcomprising: an inner ring having a deep groove inner ring racewayprovided at an outer circumferential surface of said inner ring; anouter ring having a deep groove outer ring raceway provided at an innercircumferential surface of said outer ring; and a plurality of ballsrotatably provided between said inner ring raceway and said outer ringraceway; wherein at least one of said inner ring raceway and said outerring raceway has a cross-sectional shape in which a transversely centralportion thereof is different in a radius of curvature from transverseend portions between which said transversely central portion isinterposed; and wherein transverse end edges of said portions havingdifferent radius of curvatures are made to be smoothly continuous witheach other; and wherein the radius of curvature of the transverselycentral portion is set to be in the range of 50.5% to 52% of the outsidediameter of the ball.
 2. The single row deep groove radial ball bearingaccording to claim 1, wherein the radius of curvature of thetransversely central portion is smaller than that of the transverse endportions.
 3. The single row deep groove radial ball bearing according toclaim 2, wherein the transversely central portion has a central angle inthe range of 25 to 35 degrees on each side of a center line in thetransverse direction.
 4. The single row deep groove radial ball bearingaccording to claim 3, wherein each of said transverse end portions has acentral angle in the range of 25 to 35 degrees on each side of thetransversely central portion in the transverse direction.
 5. The singlerow deep groove radial ball bearing according to claim 4, wherein saidtransversely central portion and each of said transverse end portionshave a common tangential line at a connecting portion therebetween. 6.The single row deep groove radial ball bearing according to claim 1,wherein the radius of curvature of each of said transverse end portionsis set to be in the range of 53% to 55% of the outside diameter of theball.
 7. The single row deep groove radial ball bearing according toclaim 1, wherein the radius of curvature of each of said transverse endportions is set to be in the range of 53% to 54% of the outside diameterof the ball.
 8. The single row deep groove radial ball bearing accordingto claim 1, wherein the radius of curvature of the transversely centralportion is set to be in the range of 51% to 52% of the outside diameterof the ball.
 9. The single row deep groove radial bail bearing accordingto claim 8, wherein the radius of curvature of each of said transverseend portions is set to be in the range of 53% to 54% of the outsidediameter of the ball.
 10. A single row deep groove radial ball bearingcomprising: an inner ring having a deep groove inner ring racewayprovided at an outer circumferential surface of said inner ring; anouter ring having a deep groove outer ring raceway provided at an innercircumferential surface of aid outer ring; and a plurality of ballsrotatably provided between said inner ring raceway and said outer ringraceway; wherein at least one of said inner ring raceway and said outerring raceway has a cross-sectional shape in which a transversely centralportion thereof is different in a radius of curvature from transverseend portions between which said transversely central portion isinterposed; wherein transverse end edges of said portions havingdifferent radius of curvatures are made to be smoothly continuous witheach other and; wherein the radius of curvature of each of saidtransverse end portions is set to be in the range of 50.5% to 52% of theoutside diameter of the ball.
 11. The single row deep groove radial ballbearing according to claim 10, wherein the radius of curvature of eachof said transverse end portions is set to be in the range of 51% to 52%of the outside diameter of the ball.
 12. The single row deep grooveradial ball bearing according to claim 11, wherein the radius ofcurvature of the transversely central portion is set to be in the rangeof 53% to 54% of the outside diameter of the ball.
 13. The single rowdeep groove radial ball bearing according to claim 10, wherein theradius of curvature of the transversely central portion is larger thanthat of the transverse end portions.
 14. The single row deep grooveradial ball bearing according to claim 13, wherein the transverselycentral portion has a central angle in the range of 25 to 35 degrees oneach side of a center line in the transverse direction.
 15. The singlerow deep groove radial ball bearing according to claim 14, wherein eachof said transverse end portions has a central angle in the range of 25to 35 degrees on each side of the transversely central portion in thetransverse direction.
 16. The single row deep groove radial ball bearingaccording to claim 15, wherein the radius of curvature of thetransversely central portion is set to be in the range of 53% to 55% ofthe outside diameter of the ball.
 17. The single row deep groove radialball bearing according to claim 16, wherein said transversely centralportion and each of said transverse end portions have a commontangential line at a connecting portion therebetween.
 18. The single rowdeep groove radial ball bearing according to claim 16, wherein theradius of curvature of the transversely central portion is set to be inthe range of 53% to 54% of the outside diameter of the ball.